Last week the head of the Intergovernmental Panel on Climate Change (IPCC) apologised for "a paragraph" in its four-volume 2007 report which warned there was a "very high" risk that the Himalayan glaciers, on which at least half a billion of the world's poorest people depend for water, would disappear by 2035.

"The melting goes on," said Haeberli. "It's less extreme than in years [immediately before] but what's really important is the trend of 10 years or so, and that shows an unbroken acceleration in melting."

Haeberli also repeated his warning that many glaciers are set to disappear in the next few decades, due to an expected continuation in the rise of global average temperatures. The most vulnerable glaciers were those in lower mountain ranges like the Alps and the Pyrenees in Europe, in Africa, parts of the Andes in South and Central America, and the Rockies in North America, said Haeberli.

"We are on the path of the highest scenario [of global warming] in reality, but if you take a medium scenario in the Alps about 70% will be gone by the middle of the century, and mountain ranges like the Pyrenees may be completely ice-free."

Glaciers at much higher altitudes - particularly in the Himalayas and Alaska, where it was colder and global warming could increase snowfall - could grow in the short term and were likely to last "centuries", said Haeberli. "But even for the large glaciers, for a realistic [mid-range warming] scenario, it's centuries, not millennia, and not many centuries," he added.

The WGMS records data for nearly 100 of the world's approximately 160,000 glaciers, including 30 "reference" glaciers, with data going back to at least 1980. Scientists also use methods from geology to photos and travel journals and other data to estimate glacier sizes further back in history.

The latest preliminary figures for 2007-08 show the average reduction in thickness across all the 96 glaciers was nearly half a metre, and since 1980 they have collectively lost an average of 13m thickness. During 2007-08, 30 of the 96 glaciers gained in mass.

Two years ago the WGMS preliminary figures revealed the biggest melt-rate in one year on record. The figure was later revised so it was slightly less "catastrophic" than the other extreme year in 2002-03, said Haeberli.

The IPCC uses WGMS data throughout its report, but the offending statement regarding 2035 was blamed on a quote from a scientist given to a journalist, and never presented in a peer-reviewed journal.